This description discusses draft components for railroad cars, and in particular, draft stops and their relationship to the draft sills in which they may be mounted. The discussion is made and the terminology herein is used, in the context of freight car construction and operation in North America, and, most typically, in interchange service, and in compliance with standards of construction established by the Association of American Railroads (AAR).
By their nature, railroad cars tend to be releasably linked together end-to-end in a string drawn (or pushed) by one or more locomotives. The parts of a railway car that link one car to another and permit the longitudinal loads of the train to be passed from one car to the next define the draft equipment of the railroad car. Typically, a rail road car has a body that has a center sill, whether a stub center sill or a straight-through center sill. The portion of the center sill that lies longitudinally outboard of the truck center (or last truck center, in an articulated car) may be referred to as a draft sill. The draft sill is usually a hollow column, or beam, that lies beneath a deck or shear plate of the railroad car. It usually has two parallel lengthwise extending vertical webs. A coupler, draft gear, and draft gear stops are usually mounted within the draft sill. The draft gear, as it is called, may be a sliding sill, a hydraulic end-of-car-cushioning unit (EOCC), a standard draft gear or a short travel “MiniBuff” gear. One type of draft gear may weigh about 1100 lbs, and may have, for example, about 3 inches of travel at 500,000 lbs load. The coupler is mounted to push and pull upon the draft gear. The draft gear is retained by the draft stops. The draft stops are typically mounted to the inside of the draft sill webs, and provide a means by which the force on the draft gear (received through the coupler) can be carried along the car.
There are front draft stops and rear draft stops. The front and rear draft stops are spaced apart a longitudinal distance along the draft sill corresponding to the length of the draft gear employed in the car. Rear draft stops are located within the center sill or draft sill, longitudinally inboard of the front draft stops, typically immediately outboard of the centerplate casting. Rear draft stops receive longitudinal loads from the draft gear when the coupler shank is in longitudinal compression, such as in a “run-in” condition on a descent or during humping. Rear draft stops transmit these loads into the draft sill, and most typically into the draft sill webs. The front draft stops are located further outboard toward the striker at the distal end of the draft sill whence the coupler extends. Front draft stops receive loads from the other end of the draft gear when the coupler is run out, and the coupler shank is in tension and draws on the draft gear yoke. The front draft stops transmit these loads into the draft sill, most typically into the draft sill webs. A striker, or “the striker” is the part of the car that forms the end face fitting of the draft sill. According to Railway Age's Comprehensive Railroad Dictionary, (Simmons-Boardman, Omaha, 1984) the striker is designed to be the first point of contact in the event the coupler is driven back far enough to strike the car body. The striker's function is to absorb the resulting impact and prevent damage to the center sill and surrounding area. The inventor believes that the foregoing definitions of front draft stop, rear draft stop, and striker are the customary and ordinary meanings of these terms as understood by persons skilled in the art.
This document also discusses weld fillets. The term “fillet” may be used in either of two contexts. In the first context, the “fillet” may be the empty groove, or linear notch, or angle, into which a passes, or several passes, of weld metal may be laid down. In the second sense, the term “fillet” may refer to the resulting fillet weld, or the weldmetal of that fillet weld, after the weld has been made. Although successive fillets may be laid down repeatedly to form a plug weld, the resulting accumulation of welding passes in a plug weld is usually referred to as a plug weld. Similarly, the resulting weld between two abutting plates is usually referred to as a butt weld, rather than as a fillet weld, notwithstanding that the weld may have been made by welding passes on one or both sides of the plate that were laid down as fillets.
So that the invention herein may better be understood the Applicant has included illustrations of a prior art draft gear assembly, those Figures being labeled 2a-2h. In one known assembly, the striker 58 and the front draft stops 80, 82 are formed of a single integral casting.
An example of existing rear draft stop design is shown in FIGS. 2a, 2b, 2g and 2h. The existing rear draft stop 90, 92 may tend to have a leg, or face 94, that is substantially planar, and that may tend to lie in planar abutment against the inside planar face of the side sill web 53. Web 53 has a series of parallel slots 57. The connection between web 53 and face 94 is made by clamping rear draft stop 90 or 92 in place and filling the three large, longitudinally running slots 57 with plug welds. In use, the longitudinal loads imposed on the rear draft stops are transferred through the weldmetal in shear, and into the side sill webs.
An example of an existing key slot design is shown in FIGS. 2c, 2i and 2j. In these illustrations, the monolithic combination striker and front draft stop casting, 100, includes a striker portion, identified as striker 58, and integrally formed front draft stop portions, identified as front draft stops 80, 82. The walls 85, 87 of the front draft stop that define the upper and lower boundaries of the key slot are (a) of comparable thickness to the thickness of the side sill webs, and are formed with a sharp internal corner as at 83.
In some cars there has been a tendency toward cracking of the draft sill webs at the draft stop fittings. This suggests to the inventor that attention to fatigue details and load paths in the draft stop assembly, and in the draft sill in general, may be helpful.